1. Field of the Invention
The present invention relates to a solid catalyst component for olefin polymerization, a catalyst for olefin polymerization, and a method for producing an olefin polymer. More particularly, the present invention relates to a solid catalyst component for olefin polymerization which can exhibit a high activity in polymerization of an olefin, a catalyst for olefin polymerization having a high activity using the same, and a method for producing efficiently an olefin homopolymer and copolymer using the same.
2. Description of the Related Art
As a catalyst for olefin polymerization, a Ziegler-Natta catalyst comprising a transition metal component and an organometallic component, is conventionally known. For example, as a catalyst exhibiting a high activity in olefin polymerization, there have been proposed various catalysts comprising a solid catalyst component made from a titanium compound and a magnesium compound, and an organoaluminum compound. However, when polymerization of an .alpha.-olefin such as propylene or the like, or copolymerization of ethylene with an .alpha.-olefin is conducted with the catalyst, there is a problem that low molecular weight polymers and low crystalline polymers are formed in large amount. The low molecular weight polymers and low crystalline polymers are components which exert reverse influence on transparency, impact resistance, blocking property and the like when the resulted olefin polymer is processed into a film and a sheet, therefore, it is desired to produce an olefin polymer containing little low molecular weight polymers and low crystalline polymers.
Regarding such catalysts, as a method for reducing low molecular weight polymers and low crystalline polymers, there is proposed a method in which stereoregularity is improved by allowing an electron donor such as an ester, ether or the like to be contained as an inner donor in a solid catalyst component, in the case of polymerization of an .alpha.-olefin such as propylene or the like. There is also a method proposed, for improving stereoregularity by using a catalyst comprising an electron donor such as an ester, ether, amine, organosilicon compound and or like as an outer donor, in addition to the above-described solid catalyst component and organoaluminum compound.
Further, also in the case of the copolymerization of ethylene with an .alpha.-olefin, there is proposed a method in which low molecular weight polymers and low crystalline polymers are reduced by using an electron donor as an inner donor and/or an outer donor.
However, in the method in which an electron donor is used as an inner donor and/or an outer donor, when polymerization of an .alpha.-olefin such as propylene or the like and copolymerization of ethylene with an .alpha.-olefin are conducted, reduction in formation of low molecular weight polymers and low crystalline polymers is not necessarily satisfactory.
Recently, in the field of catalysts for olefin polymerization, there is disclosed, as a new catalyst, a solid catalyst component for olefin polymerization obtained by fixing a magnesium compound and a titanium compound on a carrier composed of a polymer having a functional group.
For example, WO 94/20545 and U.S. Pat. No. 5,409,875 disclose a method for producing an ethylene-based polymer by using a catalyst comprising an organoaluminum compound and a solid catalyst component prepared by contacting an ethylene/unsaturated carboxylic acid copolymer carrier with an organomagnesium compound and a transition metal compound. Further, WO 96/30122 discloses a method for producing an ethylene-based polymer by using a catalyst comprising an organometallic compound and a solid catalyst component prepared by contacting an olefin/unsaturated carboxy acid ester copolymer carrier having specific form with an organometallic compound and a transition metal compound.
These catalysts are described to exhibit a high activity in polymerization of an olefin, especially in copolymerization of ethylene with an .alpha.-olefin. However, the ethylene/.alpha.-olefin copolymer obtained by using these catalysts was insufficient in reduction of low molecular weight and/or low crystalline components.